The present invention relates to clear air turbulence (CAT) detection systems for aircraft, in general, and more particularly, to a passive CAT detection avionics system and method which receives electromagnetic signals produced by the CAT and processes such received signals with known CAT waveform signatures to identify CAT activity and determine the position thereof with respect to the aircraft.
Air turbulence is caused by many different atmospheric conditions and may at times be dangerous to aircraft flight. Inclement weather in the form of precipitation may cause damaging air turbulence and thus, should be detected by an aircraft and avoided. For this reason, the Federal Aviation Agency (FAA) requires that weather radars be installed on all commercial aircraft. Airborne weather radars use an active radar element usually mounted in the nose of the aircraft to transmit a radar signal and receive reflections from precipitation within the range of the radar signal. The reflections are processed to detect areas of precipitation which are displayed on a display screen color coded for intensity. Thus, a pilot can view the screen, determine the severity of a storm in the flight path, and make the determination of whether or not to alter the flight path to avoid the storm.
Another dangerous form of air turbulence arises from the updrafts and downdrafts which create lightning conditions. These conditions generally arise ahead or on the edge of any associated precipitation. Accordingly, weather radar systems may not detect this form of air turbulence until it is too late to avoid it. However, lightning detection instruments, such as the Stormscope® weather mapping system manufactured by Goodrich Avionic Systems Inc. under a number of different models, for example, can detect the electromagnetic energy produced by the lightning activity and map the location thereof on a display viewable by the pilot. Thus, a complementary avionics system combining both weather radar and lightning detection should provide a viable weather mapping of any precipitation or storm related activity.
Yet another dangerous form of air turbulence occurs under tranquil and cloudless conditions, but is capable of subjecting aircraft to strong updrafts and downdrafts. This form of air turbulence is known as clear air turbulence (CAT) and has heretofore been difficult to detect with commercially viable avionics. The real danger from CAT stems from its unexpected nature. Aircraft can fly into CAT without adequate warning to its passengers. As a result, passengers may be caught without safety belt protection, and if the turbulence is severe enough, it could cause personal injury to such passengers.
Experimental models of laser based CAT detectors have been found to work with adequate range capabilities, but are too expensive to produce as a commercially viable product. Radar based systems have not had as much success. Some have proposed using electromagnetic radiation lightning detectors as a CAT detector, but such lightning detection devices use analog filtering circuits and sophisticated signal processing to accommodate the unique characteristics of lightning and thunderstorms. While enhancing the weather mapping capabilities of the lightning detection systems, this filtering and processing sophistication diminishes the usefulness of such devices for CAT detection.
Accordingly, what is needed is a commercially viable CAT avionics system which can detect CAT at sufficient distances from the aircraft to permit the pilot to alter course and avoid the turbulence, or at least provide adequate warning for the passengers to fasten their safety belts as protection against personal injury. Such a system would result in a substantial improvement to flight safety.